[gdal-dev] Re: gdal_translate -unscale option

[Chaitanya kumar CH]

John,

The 'unscale' operation computes the real value of that pixel.

-90.8230819702148 is the value stored at the pixel.
-200.277178508775 is the value of the pixel.

On Tue, Jul 26, 2011 at 5:35 AM, jt2000 <thakkar at nexgenwireless.com> wrote:

> Frank,
>
> Does the unscale option work as advertised?
>
> I have a raster with offset and scale set.
>
> Driver: GTiff/GeoTIFF
> Files: raster.tif
>       raster.tif.aux.xml
> Size is 10295, 7735
> Coordinate System is:
> PROJCS["unnamed",
>    GEOGCS["unnamed",
>        DATUM["North_American_Datum_1983",
>            SPHEROID["GRS 80",6378137,298.257222101],
>            TOWGS84[0,0,0,-0,-0,-0,0]],
>        PRIMEM["Greenwich",0],
>        UNIT["degree",0.0174532925199433]],
>    PROJECTION["Transverse_Mercator"],
>    PARAMETER["latitude_of_origin",0],
>    PARAMETER["central_meridian",-87],
>    PARAMETER["scale_factor",0.9996],
>    PARAMETER["false_easting",500000],
>    PARAMETER["false_northing",0],
>    UNIT["Meter",1]]
> Origin = (246885.000000000000000,4726455.000000000000000)
> Pixel Size = (30.000000000000000,-30.000000000000000)
> Image Structure Metadata:
>  INTERLEAVE=BAND
> Corner Coordinates:
> Upper Left  (  246885.000, 4726455.000) ( 90d 5'15.87"W, 42d38'56.20"N)
> Lower Left  (  246885.000, 4494405.000) ( 89d59'22.95"W, 40d33'42.29"N)
> Upper Right (  555735.000, 4726455.000) ( 86d19'10.68"W, 42d41'18.81"N)
> Lower Right (  555735.000, 4494405.000) ( 86d20'28.58"W, 40d35'54.87"N)
> Center      (  401310.000, 4610430.000) ( 88d11' 5.93"W, 41d38'22.21"N)
> Band 1 Block=10295x1 Type=Float32, ColorInterp=Gray
> *  NoData Value=0
>  Offset: -200,   Scale:0.00305185094759972*
>
>
> when I do a gdallocationinfo on it, i get the value of -90.82 as follows:
>
> gdallocationinfo -b 1  raster.tif 3000 3342
> Report:
>  Location: (3000P,3342L)
>  Band 1:
>    Value: -90.8230819702148
>    Descaled Value: -200.277178508775
>
> Applying unscale
>  gdal_translate -unscale -of GTiff ~/raster.tif raster2.tif
>
>  gdallocationinfo -b 1  raster2.tif 3000 3342
> Report:
>  Location: (3000P,3342L)
>  Band 1:
>    Value: -200.27717590332
>
> I would have expected -90.82 as the value.  Am I wrong?
>
> --
> View this message in context:
> http://osgeo-org.1803224.n2.nabble.com/gdal-translate-unscale-option-tp4237854p6620565.html
> Sent from the GDAL - Dev mailing list archive at Nabble.com.
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>



-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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